The project involves a characterization of the molecular defects of three temperature-sensitive, ribosome biosynthesis mutants of the eukaryote, Neurospora crassa. Two of the mutants are cold sensitive and the other is heat-sensitive; all three are characterized by an underproduction of one of the two ribosomal subunits at the nonpermissive temperature. More specifically the overall project compares the mutants with the wild type to determine if there are differences in: 1) the synthesis and processing of precursor-rRNA in whole cells and in nuclei; 2) nuclear pre-ribosomal particles; 3) protein synthetic capacity of ribosomal subunits in an in vitro protein synthesizing system; 4) ribosomal protein composition; 5) the activity of an enzyme involved with rRNA methylation, S-adenosyl methionine synthetase; 6) the nucleotide composition and number of methyl groups of the 17S rRNA.